/* 单伪元素法 */
.clearfix::after {
    content: '';
    display: block;
    clear: both;
}

/* 双伪元素法 */
.clearfix::before,
.clearfix::after {
    content: '';
    display: table;
}

.clearfix::after {
    clear: both;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

a {
    text-decoration: none;
}

li {
    list-style: none;
}